566 



Internal Waves 



Table 98 was computed with this inequality. For the various values of 

 the discontinuity in density q—q' and for the thickness of the layer h the 

 table presents the difference of velocity, which has to be exceeded, to cause 

 dynamic instability of the internal tide waves. 



Table 98. Dynamic unstable internal waves will be generated when 

 the difference in velocity u' — u in cm /sec between layers exceeds 



It can be seen from these values that even a relatively small difference of 

 velocity in the currents is sufficient, to cause instability of internal tide waves. 

 The basic currents in sea straits flow always in opposite directions in the 

 two superposed water-masses (compensating currents between ocean and 



UsC 



Fig. 236. Wave form and stream lines for dynamic unstable internal waves. II A, upper and 

 lower current having same direction; 115, upper and lower current having opposite directions. 

 Compare with Fig. 213 (V. Bjerknes). 



a mediterranean sea). The internal waves at the boundary surface in straits 

 will have therefore a particularly strong tendency towards the degeneration 

 of the wave profile and the formation of internal breakers. This is the case 

 in the Strait of Gibraltar and particularly in the Strait of Messina. 



V. Bjerknes computed for other purposes the wave form and the stream 

 lines for such unstable internal waves. Figure 236 presents two of such cases. 



